1. Field of the Invention
The present invention relates to a developing device used in an image forming apparatus such as an electrophotographic printer, and more particularly relates to a developing device which develops latent images on a surface of a latent image holding body.
2. Description of the Related Art
In an electrophotographic printer, such as a laser printer, a surface of a latent image holding body, such as a photosensitive drum, is exposed by light from an exposing unit including an optical system so that a latent image (an electrostatic latent image) is formed. The latent image formed on the surface of the latent image holding body is developed. An image obtained by the development is transferred to a paper, so that a print is made on the paper.
In a developing device used in such a printer, developer (e.g., toner) is conveyed by a developing roller and supplied to the latent image holding body. The latent image formed on the latent image holding body is then developed by the developer and a visual image is formed.
There are two developing methods; a dual-component developing method and a mono-component developing method. In the dual-component developing method, dual-component developer made of toner and carriers is used. In the mono-component developing method, only toner is used as the developer.
According to the dual-component developing method, a large amount of toner can be conveyed. The dual-component developing method is thus suitable for a printer for which a high-speed print operation is required.
According to the mono-component developing method, although a small amount of toner can be conveyed, a structure of a printing process unit can be miniaturized. The mono-component developing method is suitable for a miniaturized printer.
Further, a method for improving the printing speed in a miniaturized printer is proposed in Japanese Laid Open Patent Application No. 3-174175. In such a method, the carriers exist only surrounding the developing roller and toner is supplied to the latent image holding body via the carriers for the development. The toner is supplied from a toner container behind the developing roller to the carriers surrounding the developing roller.
Although the printer for which the high-speed printing operation is required can be miniaturized by using the conventional developing device operating in accordance with the method as described above, it may be required for the conventional developing device to improve the quality and definition of images.